1. Field of the Invention
The present invention relates to a method of forming emitter tips for use in a field emission display. In particular, the present invention relates to the fabrication of emitter tips including insulating tips with a molybdenum metal layer thereon.
2. Description of the Related Art
FIG. 1 shows a cross-section diagram of a field emission display in the prior art. A conductive cathode 13, an insulating layer 16, and a dielectric layer 11 are formed on a substrate 10. A plurality of emitter tips 2 are formed on the insulating layer 16, connecting to a tip cavity 3 and an opening 4 nearby. A gate electrode 5 and a contact layer 7 are formed on the dielectric layer 11. A conductive layer 18 and an interval 8 are formed on the contact layer 7. An anode plate 9 is formed on the interval 8 in which is opposed to the gate electrode 5 and the emitter tips.
Fowler and Nordheim proposed the earliest emission theory. The following current emission equation is derived from the Quantum Mechanics:   I  =                    α        ⁢                  xe2x80x83                ⁢        A        ⁢                  xe2x80x83                ⁢                  β          2                ⁢                  V          2                            Φ        ⁢                  xe2x80x83                ⁢                  t          2                      ⁢          exp      ⁡              [                              -                          Bv              ⁡                              (                y                )                                              ⁢                                    Φ                              3                2                                                    β              ⁢                              xe2x80x83                            ⁢              V                                      ]            
xcex2: ratio in electric field
"PHgr": work unction in electrode material
t: time
V: applied voltage
Referring to FIG. 1, emitter tips emit electrons by increasing the applied voltage into the region between the gate electrode 5 and emitter tips 2 until the equation above is met. After electrons from emitter tips 2 pass by the opening 4, the electrons are attracted by the anode plate 9 and start accelerating. Thereby electron bombardment activity on the surface of anode plate 9 containing luminescence powder (not shown) takes place. The luminescence powder being bombarded by electrons begins to radiate. The light beam, formed by radiation, passes through the anode plate 9 and emerges onto the opposite side of the anode plate 9, the emission display panel.
A cathode panel of field emission display in the prior art, having six thin films, requires six lithography and etching process runs.
FIG. 2A to FIG. 2E illustrate the fabrication in field emission display of the prior art. The fabrication steps are deposition, etching, sputtering, and lift-off. FIG. 2A illustrates a cathode conductive layer 13, a dielectric layer 11, an insulating layer 16, and a gate electrode layer 5 formed onto a substrate 10 in sequence. An opening 4 of about one micron in width is formed within the gate electrode layer 5. FIG. 2B, a cavity is formed inside the dielectric layer with conventional etching. The cavity is about two microns wide.
As shown in FIG. 2C, the sputtering for an aluminum metal layer 19 is performed by inclining the panel to an angle, for example, at 20 degree.
As shown in FIG. 2D, after the aluminum metal layer 19 is formed on the gate electrode layer 5, a molybdenum metal layer 20 is sputtered onto the aluminum metal layer 19 and the dielectric layer 11 respectively. When the molybdenum metal layer 20 and the aluminum metal layer 19 on the gate electrode layer 5 are removed with phosphoric acid, a cone-like emitter tip made of molybdenum metal is formed, as shown in FIG. 2E.
However, molybdenum is very expensive. To save cost, therefore, it is desirable to reduce the amount of molybdenum consumed during the emitter tips fabrication.
The present invention provides a method of forming emitter tips for use in a field emission display. A first dielectric layer, an insulating layer, and a conductive layer are formed on a substrate in sequence. An opening and a tip cavity are formed in the conductive layer. An insulating tip is formed on the first dielectric layer. Finally, a molybdenum metal layer on the insulating tip is formed. The method of the present invention can substantially reduce the consumption of molybdenum.